The present invention relates to fuel cells, such as solid high polymer fuel cells, phosphoric acid fuel cells and methanol fuel cells, which are operated at a relatively low temperature, and more particularly to improvements in the oxidizer gas discharge channels of oxidizer plates of such cells.
Solid high polymer fuel cells, phosphoric acid fuel cells and methanol fuel cells are known as fuel cells which are operated at a relatively low temperature.
Of these fuel cells, the construction of the solid high polymer fuel cell will be described generally with reference to FIG. 1 showing an embodiment of the invention.
FIG. 1 shows a cell unit 10 of a solid high polymer fuel cell device. The cell unit 10 comprises a cell 12 which is held between an oxidizer plate 26 and a fuel plate 56. The fuel cell device usually comprises tens to hundreds of cell units 10.
The cell 12 comprises an electrolytic membrane for use as an electrolytic member 14, an anode 50 formed on one side of the membrane, and a cathode 20 formed on the other side thereof.
The fuel plate 56 has a fuel chamber 54 positioned at the anode side of the cell 12 and formed by gas channels 52 for passing a fuel gas therethrough.
With reference to FIG. 7, the oxidizer plate 26 has an oxidizer chamber 24 formed at the cathode side thereof and comprising gas channels 22 for passing an oxidizer gas therethrough. Communicating with the oxidizer chamber 24 are oxidizer supply channels 28 for introducing an oxidizer gas into the oxidizer chamber 24, and oxidizer discharge channels 30 formed at opposite side to the supply channels 28 for discharging to the atmosphere the oxidizer exhaust gas resulting from a reaction.
With the solid high polymer fuel cell device thus constructed, a fuel gas containing hydrogen gas is supplied to the fuel chamber 54, and air or like oxidizer gas containing oxygen is supplied through the oxidizer supply channels 28 to the oxidizer chamber 24, and an electrochemical reaction between the fuel gas and the oxidizer gas generates an electromotive force and produces water.
The oxidizer exhaust gas discharged from the oxidizer chamber 24 contains the water produced by the reaction and humidifying water (including water migrating from the fuel chamber) admitted for giving moisture to the electrolytic member 14. The oxidizer chamber 24 (reaction zone) in which the electrochemical reaction proceeds generates heat due to the reaction and is therefore less likely permit condensation of water vapor, whereas the oxidizer discharge channel 30 outside the reaction zone has a lower temperature, permitting condensation of water vapor in the oxidizer exhaust gas to block the discharge channel 30. If the discharge channel 30 is blocked, there arises the problem that the oxidizer gas no longer passes through the corresponding gas channel 22, impeding the progress of the electrochemical reaction and impairing the cell performance.
This problem is encountered not only with solid high polymer fuel cells but also with fuel cells, such as phosphoric acid fuel cells and methanol fuel cells, which are operated at a relatively low temperature.
Accordingly, a fuel cell has been disclosed wherein as shown in FIG. 8, a groove extending from an oxidizer supply channel 28 to an oxidizer discharge channel 30 and providing these channels is given a gradually increasing depth to prevent stagnation of water (JP-A No. 138696/1996). However, this structure has the likelihood that in the vicinity of the oxidizer discharge channel 30, the flow channel has an increased cross sectional area, which decreases the speed of flow of the oxidizer gas, rendering water liable to stagnate undesirably. Furthermore, an increase in the depth of the flow channel entails the problem that the oxidizer plate 26 needs to have an increased thickness, giving an increased thickness to the cell unit 10 to make the cell assembly large-sized. If the plate 26 has a thick portion and a thin portion due to the difference in the depth of the flow channel, the cell will have uneven internal resistance in its plane, consequently leading to an uneven distribution of current densities and entailing the likelihood of lower cell voltage.
An object of the present invention is to provide a fuel cell device having oxidizer discharge channels adapted to prevent water from stagnating therein and thereby prevented from being blocked to assure the fuel cell device of an improved cell life and stabilized electricity generating performance.
To fulfill the above object, the present invention provides a fuel cell device which comprises a plurality of cell units arranged in superposed layers and each comprising a cell having an anode formed on one surface of an electrode member and a cathode formed on the other surface of the electrode member, a fuel plate having a fuel chamber formed by a gas channel for passing a fuel gas therethrough, and an oxidizer plate having an oxidizer chamber formed by a gas channel for passing an oxidizer gas therethrough, an oxidizer supply channel for supplying the oxidizer gas to the oxidizer chamber and an oxidizer discharge channel for releasing to the outside air an oxidizer exhaust gas discharged from the oxidizer chamber, the cell being sandwiched between the two plates, with the fuel chamber facing the anode of the cell and with the oxidizer chamber facing the cathode thereof. The oxidizer discharge channel has a first opening in communication with the oxidizer chamber and a second opening in communication with the outside air, the second opening being smaller than the first opening in width.
When the cell units are arranged approximately horizontally in juxtaposed layers, with the gas channel of the oxidizer chamber positioned approximately horizontally, the oxidizer discharge channel may have its second opening positioned at a lower level than the first opening. In this arrangement, it is also desired that the second opening be smaller than the first opening in width.
The second opening at the outer end of the oxidizer discharge channel has a smaller width than the first opening at the inlet of the discharge channel and therefore increases the gas pressure at the outlet end of the channel, permitting the oxidizer gas to flow out at a higher speed. Even if water vapor condenses in the oxidizer discharge channel, the resulting water is accordingly forced out from the discharge channel without blocking the channel. The increased gas pressure at the outlet end of the discharge channel increases the pressure of the oxidizer gas in gas channels when more than one gas channel is provided, evenly distributing the oxidizer gas over the channels to give a higher cell voltage.
Further with the second opening positioned at a lower level than the first opening, water will move toward the second opening under gravity for discharge to the outside, if formed in the discharge channel on condensation and deposited in the channel. This eliminates the likelihood of the discharge channel becoming blocked.
Because the second opening has a smaller width than the first opening and is positioned at a lower level than the first opening, the water in the discharge channel is drawn off to the outside by virtue of the increased gas pressure and the gravity acting on the water, whereby the discharge channel is prevented from being blocked more reliably.